The present invention relates to a vehicle position calculation apparatus and method for accurately determining a vehicle position on a map route in a navigation system for a vehicle.
In such a vehicular navigation system, it has been a usual practice to utilize a vehicle position calculation apparatus which employs a map matching technique for calculating a vehicle position to be displayed on a map route.
The map matching technique strictly operates on an assumption in that the vehicle travels on the road. In particular, measuring sensors include a GPS receiver, a gyro sensor and a vehicle speed sensor which provide a vehicle position and a vehicle travel direction. The vehicle position and the vehicle travel direction are compared with a group of line segments, representing a road shape, which are preliminarily stored in a memory section, thereby correcting the vehicle position so as to lye on a particular point on the line segment having the most probable relationship in a position and a direction in conjunction with the measured value.
Firstly, a vehicle position correction method in the related art is described below in detail with reference to a branch road shown in FIG. 22 to exemplify how correction of the vehicle position is performed in the branch road.
In FIG. 22, it is assumed that the branch road B is given as a correction shape for the vehicle position and is constructed of three line segments L1, L2, L3 connected with each other and diverging at a node N. In this respect, it is a usual practice to define a road shape with a plurality of nodes determined at respective positions (with latitude and longitude) and line segments representing a connecting relationship relative to the respective nodes. The road shape thus defined in such a configuration is used for effectuating a map matching operation as will be hereinafter described in detail.
In FIG. 22, points P1 to P7 refer to measured values or measured points of the vehicle position which is measured with the measuring sensors at time instants t1 to t7. Also, points Q1 to Q7 refer to corrected and outputted vehicle positions which are extracted in the vehicle position calculation of the related art. In actual practice, the measured values of the vehicle position are obtained by the measuring sensors to directly provide the coordinate value Pn in an absolute value or to individually provide a vehicle travel direction xcex8nxe2x88x921, n and a traveled distance xcexnxe2x88x921, n in a relative value between associated measuring points.
In the former case, the point Pn which is directly measured is hereinafter referred to as a primary vehicle position. In the latter case, also, assuming that a previous measured value is Pnxe2x88x921, an absolute coordinate value Pn is given by:
Pn=Pnxe2x88x921+xcexnxe2x88x921, n exp(ixcex8nxe2x88x921, n)xe2x80x83xe2x80x83(1) 
wherein exp is an index factor and i is an imaginary unit.
The vehicle position thus obtained is hereinafter referred to as a secondary vehicle position.
The primary and secondary vehicle positions are collectively called as a measured value of the vehicle position. Even in the former case, it is possible to calculate back the relative displacement value xcex8nxe2x88x921, n and xcexnxe2x88x921, n from the above equation (1).
Now, at the time instant t1, the measured value P1 of the vehicle position substantially lies on the line segment L1 and, because a previous vehicle travel direction is substantially aligned with a direction of the line segment L1, the measured point P1 and a corrected result Q1 are assumed to lye on the same point.
Next, at the time instant t2, the measured value of the vehicle position has the point P2 which is dislocated from the line segment L1. If, in this instance, there is no line segment, in close proximity to the measured point, for correcting the vehicle position, except for the line segment L1 and the vehicle travel direction Q1, 2 is oriented at an angle within an allowable error range, then, it is assumed that the vehicle travels on the same road as that the vehicle has previously traveled. That is, it is discriminated that the vehicle position at the time instant t2 still lies on the line segment L1. Accordingly, the vehicle position at this time instant is corrected to a point Q2 at which a leg of a vertical line drawing from the point P2 intersects the line segment L1.
Further, at the time instant t3, it is assumed that the point P3 is given as the primary vehicle position, or the vehicle travel direction xcex82, 3 and the traveled distance xcex2, 3 are obtained between the time interval t2, t3. At the previous time instant t2, the vehicle position is corrected at the point Q2 on the line segment L1. In such a case, assuming that the degree of precision of the relative displacement value is guaranteed to some extent, then, the point P3xe2x80x2 is obtained as the secondary vehicle position on the basis of a reference of the previous corrected value as expressed by:
P3xe2x80x2=Q2+xcex2,3exp(ixcex82,3)xe2x80x83xe2x80x83(2) 
Here, if the point P3xe2x80x2 does not lye on the line segment L1, then, the measured point of the vehicle position is corrected at the point on the line segment L1 in the same manner as that achieved in the previous case. For example, the correction is implemented by drawing the leg of the vertical line from the point P3xe2x80x2 to the line segment L1 to output the corrected point Q3 as a final corrected position. At subsequent steps after the time instant t3, similar operations are carried out.
In accordance with the vehicle position calculation method discussed above, as far as a premise satisfies that the vehicle travels on the road, even when the output value of the measuring sensor contains a slight amount of detection error, the detection error is corrected to accurately align the vehicle position with a correct position of the map route in a reliable manner.
Besides, in another related art, it has been proposed that a vehicle position calculation apparatus employs a CD-ROM, which preliminarily stores a plurality of road links with a road being represented with line segments, to enable map matching operation to allow the road links in the vicinity of the vehicle position to be read out from the CD-ROM such that the vehicle position is forced to lye on the road link.
However, in the first related art discussed above, in a case where the road shape which serves as a ground for correction of the vehicle position is different from an actual road shape, correction of the vehicle position causes a cumulative error, with a resultant output of an erroneous vehicle position.
More particularly, as seen in FIG. 22, an actual road shape has an increased road width in front of a branching point and the vehicle, which tends to travels on the line segment L3, is supposed to be closer to the left side than the line segment L1 fairly in front of the node N during traveling. Such a structure is found in the road which has a lane for deceleration of the vehicles at a location in which an exit road diverges from a main road such as an interchange in high-way road.
As a consequence, the measured values P1 to P7 shown in FIG. 22 show a position rather closer to an actual road when the vehicle is going to get out the line segment L3. However, in accordance with the former related art, the map matching technique causes the vehicle position to be corrected with respect to the main road. That is, during the time period between t1 to t5, the respective measured points of the vehicle position are corrected at the corrected points Q1 to Q5 on the line segment L1.
However, at the time instant t6 shown in FIG. 23, even if the measured point P6 is given under a condition that the accuracy of the relative displacement value is guaranteed, the previous correcting position Q5 is used as the reference based on which the secondary vehicle position is extracted at the point P6xe2x80x2 which lies on the position in the vehicle travel direction xcex85,6 with the traveled distance xcex5,6.
Here, the measured point P6xe2x80x2 is not aligned with any one of the line segments L1, L2, L3 and, therefore, a further correction is implemented. In such a case, correcting position candidates are located on two points Q6, Q6xe2x80x2 of legs of the vertical lines drawn from the point P6xe2x80x2 to the line segments L2, L3. Actually, assuming that the vehicle is traveling in a region closer to the left side fairly in front of the time instant t6 with a view to leaving to the exit line segment L3, since a steering angle is varied in a relatively gradual manner, it is deemed that the vehicle travel direction at such a time instant is in a forward direction, i.e. to be closer to a direction along the line segments L1 to L2.
If so, the secondary vehicle position P6xe2x80x2 is closer to the point Q6 among the two candidate points, with a resultant correction of the vehicle position onto the point Q6 on the line segment L2 at the time instant t6. Further, at the time instant t7, the measured point P7 is corrected to the point Q7 on the line segment L2 in the similar manner as previously described above.
Thus, in accordance with the vehicle position calculation apparatus in the first related art, the vehicle position, which is deemed to exit from the main road, is inevitably corrected to the point on the main road. Especially, in a Y-shaped road where two diverging roads constitute an acute angle, an issue is encountered in correction of the vehicle position for the same reasons as previously discussed above.
Next, in the second related art discussed above, with such a vehicle position calculation apparatus, the road links stored in the CD-ROM is represented with a single line which passes through a substantially center of the road without distinction of the ups and downs of the road in case of no median strip.
For this reason, when the map matching operation is performed in conjunction with a wide road with a large width, since the vehicle position is forcibly located on the road link located on the central line of the road, the vehicle position is inevitably dislocated from the correct position in fore and aft directions immediately after the vehicle turns to the left or the right.
For example, as shown in FIG. 24A, it is assumed that the vehicle turns to the left at an intersecting point a and, thereafter, goes forward through an intersecting point b to an intersecting point c, at close range from the point b, at which the vehicle further turns to the left at a second time. In such a case, the traveling distance due to actual traveling locus becomes shorter than the distance of the traveling link involving the intersecting points a, b, c. As a result, when performing the map matching operation, the apparatus suffers from an undershooting effect to cause the vehicle position to be wrongly corrected such that the vehicle turns to the left at the intersecting point b shorter in distance than the intersecting point c during actual turning of the vehicle to the left as seen in FIG. 24B.
As seen in FIG. 25A, further, it is assumed that the vehicle turns to the right at the intersecting point a and, thereafter, the vehicle turns to the right at the intersecting point b at the second time. In such a case, the traveling distance due to actual traveling locus becomes longer than the distance of the traveling link involving the intersecting points a, b. As a result, when performing the map matching operation, the apparatus suffers from an overshooting effect to cause the vehicle position to be wrongly corrected such that the vehicle turns to the right at the intersecting point c shorter in distance than the intersecting point b during actual turning of the vehicle to the right as seen in FIG. 25B.
It is therefore an object of the present invention to provide a vehicle position calculation apparatus and a vehicle position calculation method which are able to accurately correct a vehicle position in accordance with an actual road state.
It is another object of the present invention to provide a vehicle position calculation apparatus and a vehicle position calculation method which are able to accurately correct a vehicle position even when a vehicle turns to the left or the right at an intersecting point.
According to a first aspect of the present invention, there is provided a vehicle position calculation apparatus having: a vehicle position measuring section measuring a vehicle position; a road data supply section supplying road geometrical data including a line segment and a closed region correlated with a road on a map; and a vehicle position correcting section correcting the vehicle position on the map by using the road geometrical data. The position correcting section locates the vehicle position by itself on the map as a corrected vehicle position, in response to a relatively positional relation between the vehicle position and the road geometrical data.
Also, in such a structure, the vehicle position correcting section can correct the vehicle position to be in alignment with a point on corresponding one of position correction shapes composed of a group of line segments representing a center of a road and a two-dimensional closed regional shape correlated with a predetermined location.
Still also, in such a structure, the vehicle position correcting section can correct the vehicle position onto a traveling link generated in response to the road geometrical data.
In other words, there is provided a vehicle position calculation apparatus having: measuring means for measuring a vehicle position; supplying means for supplying road geometrical data including a line segment and a closed region correlated with a road on a map; and correcting means for correcting the vehicle position on the map by using the road geometrical data. The correcting means locates the vehicle position by itself on the map as a corrected vehicle position, in response to a relatively positional relation between the vehicle position and the road geometrical data.
According to a second aspect of the present invention, there is provided a vehicle position calculation apparatus having: a vehicle position measuring section measuring a vehicle position; a position correcting shape memory section storing road shape data including position correction shapes composed of a group of line segments representing a center of a road and a two-dimensional closed regional shape correlated with a predetermined location on a map; and a vehicle position correcting section correcting the vehicle position on the map to be in alignment with a point on corresponding one of the position correction shapes stored in the position correcting shape memory section. The vehicle position correcting section includes: a correction reference determination unit determining whether to correct the vehicle position based on a reference of any one of the position correcting shapes stored in the position correcting shape memory section, on the basis of a close proximity or inclusive relationship between the vehicle position and the any one of the position correcting shapes; a line segment conformity position correcting unit correcting the vehicle position so as to allow the vehicle position to be aligned onto a point of the line segment which the correction reference determination unit determines as the reference; and a regional conformity position correcting unit correcting the vehicle position so as to allow the vehicle position to be aligned onto a point inside the closed regional shape or on a point of a contoured line segment of the closed regional shape which the correction reference determination unit determines as the reference.
According to a third aspect of the present invention, there is provided a vehicle position calculation apparatus having: a vehicle position measuring section measuring position information representing a vehicle position and bearing information representing a vehicle travel direction; a road map memory section storing road shape data composed of polygons correlated with a road on a map; an attribute data memory section storing joint attribute data representing traffic regulating information with respect to the road shape data and a joint state information between the road shape data; a map read out section reading out the road shape data in a vicinity of the vehicle position and the joint attribute data from the map read out memory section and the attribute data memory section, respectively, on the basis of the position information; a traveling link generating unit generating a traveling link correlated with the vehicle position in response to the road shape data and the joint attribute data read out by the map read out section, on the basis of the position information and the bearing information; and a vehicle position correcting section responsive to the position information and the bearing information to correct the vehicle position on the map onto the traveling link generated by the traveling link generating unit.
Besides, in the present invention, a vehicle position calculation method measures a vehicle position; supplies road geometrical data including a line segment and a closed region correlated with a road on a map; corrects the vehicle position on the map by using the road geometrical data; and locates the vehicle position by itself on the map as a corrected vehicle position, in response to a relatively positional relation between the vehicle position and the road geometrical data.
Other and further features, advantages, and benefits of the present invention will become more apparent from the following description taken in conjunction with the following drawings.